1. Field of the Invention
The present invention relates to a vehicle lane detector and a method for detecting a lane sign on a road surface.
2. Description of the Related Art
Conventionally known vehicle lane detectors detect a lane sign drawn on a road surface on which a vehicle drives. The vehicle lane detector detects a lane sign to be used for a driving support system that executes a lane keeping operation, i.e., an operation to keep the vehicle inside the lane, based on the lane sign, or for a deviation warning system that detects lateral shifts of the vehicle based on the lane sign and gives a warning when the result of detection indicates that the vehicle is likely to derail the lane. Here, the lane sign means a sign that indicates a lane boundary such as a line that separates lanes, white lines or yellow lines, for example, as well as a vehicle guiding sign, such as a dotted-line sign, that is provided to draw drivers' attentions.
For more detailed information on conventional techniques, see Japanese Patent Application Laid-Open Nos. H8-320997 and 2001-14595.
When the road is covered with snow, wet, or dirty, the lane sign cannot be clearly seen. When there are different types of lines on the road surface, as in the city, or there is no lane sign and curbs are provided on the road shoulders, the error in lane sign detection (including “lost”, that is failure of detection) is likely to happen. Then, due to detection error or the repetition of detection and “lost”, the driving support system or the deviation warning system may be repeatedly switched between ON and OFF, or the deviation warning system may erroneously raise an alarm.